The invention relates to a device for inductively charging a vehicle.
Vehicles with an electric drive typically have a battery in which electrical energy for operating an electrical machine of the vehicle can be stored. The battery of the vehicle can be charged with electrical energy from an electrical power supply system. For this purpose, the battery is coupled to the electrical power supply system in order to transmit the electrical energy from the electrical power supply system to the battery of the vehicle. The coupling can be implemented using wires (by means of a charging cable) and/or in a wireless manner (using an inductive coupling between a charging station and the vehicle).
One approach for automatic, cable-free, inductive charging of the battery of the vehicle involves transmitting the electrical energy to the battery from the floor to the underbody of the vehicle by means of magnetic induction across the underbody ground clearance 120. This is illustrated, by way of example, in FIG. 1. In particular, FIG. 1 shows a vehicle 100 with a storage device 103 for electrical energy (e.g. with a chargeable battery 103). The vehicle 100 has what is referred to as a secondary coil in the underbody of the vehicle, wherein the secondary coil is connected to the storage device 103 by means of an impedance matching arrangement, not shown, and a rectifier 101. The secondary coil is typically part of what is referred to as a “wireless power transfer” (WPT) vehicle unit 102.
The secondary coil of the WPT vehicle unit 102 can be positioned above a primary coil, wherein the primary coil is mounted, for example, on the floor of a garage. The primary coil is typically part of what is referred to as a WPT floor unit 111. The primary coil is connected to a power supply 110 (in this document also referred to as charging unit 110). The power supply 110 can comprise a radiofrequency generator, which generates an AC (Alternating Current) in the primary coil of the WPT floor unit 111, as a result of which a magnetic field is induced. This magnetic field is also referred to as an electromagnetic charging field in this document. The electromagnetic charging field can have a predefined charging-field frequency range. The charging-field frequency range (i.e. the operating frequency) can lie in the frequency range of 80-90 kHz (in particular at 85 kHz).
Given sufficient magnetic coupling between the primary coil of the WPT floor unit 111 and the secondary coil of the WPT vehicle unit 102 across the underbody ground clearance 120, the magnetic field induces a corresponding voltage and therefore also a current in the secondary coil. The induced current in the secondary coil of the WPT vehicle unit 102 is rectified by the rectifier 101 and stored in the storage device 103 (e.g. in the battery). It is therefore possible to transmit electrical energy in a cable-free manner from the power supply 110 to the energy storage device 103 of the vehicle 100. The charging process can be controlled in the vehicle 100 by a charging controller 105 (also referred to as a WPT controller 105). To this end, the charging controller 105 can be configured to communicate, for example in a wireless manner, with the charging unit 110 (e.g. with a wall box) or with the WPT floor unit 111.
Various systems for inductively charging electric vehicles are currently being developed. Here, in particular, various designs for the geometric arrangement of the coils and the associated field geometry (e.g. circular coils, solenoid coils or double-D coils) are being pursued. On account of the different geometric arrangements, there may be incompatibilities between the secondary coil that is built into a vehicle 100 and the primary coil that is built into a floor unit 111. Incompatibilities of this kind may result in a reduced (or even non-existent) coupling between the primary coil and the secondary coil and thus in a reduced (or even non-existent) energy transfer. Furthermore, when using coils having different coil geometries, the demands on precise positioning of the primary coil and the secondary coil are further increased.
The present document concerns the technical problem of providing a cost-effective primary coil that enables an increased degree of compatibility with secondary coils and/or enables reduced demands on the positioning of secondary coils.
The problem is solved by providing a primary unit in accordance with embodiments of the invention.
In accordance with one aspect, a primary unit for generating an electromagnetic charging field for inductive coupling to a secondary coil is described. The primary unit may be part of a WPT floor unit of a charging station for inductively charging an energy storage device of a vehicle. That is to say that the primary unit may be configured to inductively charge an electrical storage unit of a vehicle.
The primary unit includes a multipartite primary coil, which includes N coil elements, where N>2. The N coil elements are coupled to one another in a star configuration at a respective first end. The N coil elements may comprise or be N circular coil elements, wherein the N circular coil elements may be arranged laterally alongside one another in one plane.
By way of example, it is possible that N=3. The N coil elements then include a first coil element, a second coil element and a third coil element. The first coil element may be arranged on a first side of the second coil element and the third coil element may be arranged on a second side of the second coil element, said second side lying opposite the first side of the second coil element. A charging field for different types of secondary coil can be generated efficiently by means of a multipartite primary coil of this type. Furthermore, it is possible to compensate for a lateral offset between the multipartite primary coil and the secondary coil.
In a further example, N=5. The N coil elements may include a central coil element, which is surrounded by four further coil elements. A charging field for different types of secondary coils can be generated efficiently by a multipartite primary coil of this type as well. Furthermore, it is possible to compensate for a lateral offset and an offset in the longitudinal direction between the multipartite primary coil and the secondary coil. In addition, it is possible to compensate for relative rotations between the primary coil and the secondary coil.
The primary unit further includes N half-bridges, which in each case are coupled to a respective second end of the N coil elements. Here, the second end of a coil element is opposite the first end of the coil element. Each coil element is therefore connected to a corresponding half-bridge. A half-bridge is typically configured to couple the second end of a coil element alternately to a first potential (e.g. to ground) and to a second potential (e.g. to a supply voltage or to a DC voltage derived from the supply system voltage). By alternately coupling the second end of the coil element to different potentials, an alternating current that induces an electromagnetic charging field can be generated in the coil element. On the other hand, the switches of a half-bridge can also be kept open in order to prevent a current through the corresponding coil element.
The primary unit further includes a control unit, which is configured to drive the N half-bridges depending on the secondary coil. In particular, the control unit may be configured to drive the N half-bridges depending on a type of the secondary coil and/or depending on a position of the secondary coil relative to the multipartite primary coil. Examples of types of the secondary coil are a solenoid type, a double-D type and/or a circular type. A charging field for a multiplicity of different types of secondary coils can therefore be generated efficiently by the primary unit, said charging field inducing a charging current in the secondary coil. The primary unit is particularly cost-effective as only one half-bridge is used for each coil element.
The primary unit may furthermore include N capacitors. The N capacitors may be arranged in each case in series with the N coil elements. A capacitor may, together with a coil element, form a resonant circuit. A resonant frequency of the resonant circuit may correspond to the charging frequency of the charging field generated by the primary unit.
The control unit may be configured to operate at least two of the N half-bridges mutually in differential mode. An alternating current through the at least two corresponding coil elements of the multipartite primary coil is therefore possible. Furthermore, it is possible for a current to flow through the at least two coil elements in the opposite direction. Alternatively or in addition, the control unit may be configured to operate at least two of the N half-bridges mutually in common mode. It is therefore possible, when a current flows through the corresponding coil elements, for the current through the corresponding coil elements to have the same direction (i.e. from the second end to the first end of the coil element or vice versa). Alternatively or in addition, the control unit may be configured to operate at least one of the N half-bridges in such a way that no current flows through the corresponding coil element. The corresponding coil element can therefore be excluded from the generation of an electromagnetic charging field.
By operating the half-bridges in differential mode, in common mode and/or by deactivating a half-bridge, it is possible to generate different geometries of charging fields efficiently. The primary unit may therefore be adapted to different types of secondary coils and/or to different offset situations.
The control unit may be configured to operate at least two of the N half-bridges with a charging frequency, wherein the charging frequency corresponds to a frequency of the electromagnetic charging field. In particular, the at least two half-bridges may be operated in differential mode with the charging frequency in order to generate an alternating current with the charging frequency through the corresponding coil elements. For differential mode operation, a “low side” switch of a first half-bridge may be closed when a “high side” switch of a second half-bridge is closed (the “high side” switch of the first half-bridge and the “low side” switch of the second half-bridge are then open). Furthermore, the “high side” switch of the first half-bridge may be closed when the “low side” switch of the second half-bridge is closed (the “low side” switch of the first half-bridge and the “high side” switch of the second half-bridge are then open).
The control unit may be configured to determine a type of the secondary coil (e.g. the type of the secondary coil may be communicated from a vehicle to a charging station in the context of charging communication). Furthermore, the control unit may be configured to determine predefined operating data for the N half-bridges depending on the determined type of the secondary coil. The predefined operating data may be stored in a storage unit (e.g. in a storage unit of the charging station). The predefined operating data may be stored in the form of a characteristic diagram and/or in the form of a table. In particular, different predefined operating data may be stored for different types of secondary coil. The control unit may then be configured to drive the N half-bridges in accordance with the predefined operating data. It is therefore possible to adapt the operation of the primary unit to the type of secondary coil efficiently.
The control unit may be further configured to determine the position of the secondary coil relative to the multipartite primary coil. Here, the position may comprise a lateral offset between the secondary coil and the multipartite primary coil. The relative position may be determined, for example, by evaluating image data. For this purpose, the primary unit may optionally include a camera, which is configured to capture image data regarding the secondary coil. The predefined operating data may then also be determined depending on the determined position. It is therefore possible to adapt the operation of the primary unit to different offset situations efficiently.
In accordance with a further aspect, a charging station for a vehicle is described, wherein the charging station includes a primary unit that is described in this document.
It should be noted that the methods, devices and systems that are described in this document may be used both alone and in combination with other methods, devices and systems that are described in this document. Furthermore, any aspects of the methods, devices and systems that are described in this document may be combined with one another in a variety of ways. In particular, the features of the claims may be combined with one another in a variety of ways.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.